Landslide Taxonomy and Vulnerability in Eastern Bhutan

Landslide is observed in almost all parts of the world, particularly along the unstable slope, but it may happen even in plain areas in some situations. Understanding the conditions of the landslide area/pocket concerned is of prime importance to know the causes of landslide. Landslide vulnerability is determined depending on the nature of slope, rock/earth/soil found, and cohesiveness and consolidation among themselves as well as the amount of moisture present. Based on the types of materials involved, slope gradient, water content, and mode of movement, landslide is categorized into various groups. Landslide is generally associated with and due to heavy rainfall, cloud burst and flash floods, rapid snow-melt, geology of the area, removing the materials from the base, i.e., road construction, heavier load at the top, uncontrolled irrigation above the hilly roads, poor forest management, erosion, etc. An earthquake even of lesser intensity may escalate the disastrous landslide into catastrophic proportion. Eastern Bhutan (about 11400 square km) with mountainous terrain is very susceptible to landslides and particularly those associated with earthquake. The occurrence of earthquake in combination with heavy rain in monsoon months aggravates the damage done due to landslide. This paper attempts to categorize landslide into various groups based on variations and also assess the vulnerability of Eastern Bhutan to landslides.